Circuit for prolonging the life of fluorescent lamps

ABSTRACT

A circuit for extending the life of fluorescent tubes driven from a power source subject to interruptions, which includes a uni-directional conducting elements inserted in the line from the power source, a separately powered power source of substantially lower voltage than the main power source but of sufficient voltage to maintain the fluorescent tube in conduction, a second uni-directional device connected between the secondary power source and the common junction of the first uni-directional device and the load. Further, the circuit may include a voltage sensor to determine whether or not the power is present on the primary power source, a timer to time the length of time during which power is missing, and means of disconnecting the secondary power source when such time is excessive.

United States Patent [1 1 Tomsky et al.

[4 Dec. 31, 1974 [54] CIRCUIT FOR PROLONGING THE LIFE OF 3,566,186 2/1971 Woolsey 315/ 160 FLUORESCENT LAMPS Primary Examiner-Harold A. Dixon 7 1 t H W. T k B H G. 5] men Ors 352 z g l gg sf Attorney, Agent, or Fzrrn-Im1r|e, Smiley & Linn [73] Assignee: CML-Macarr, lnc., Edison, NJ. by

said Harry W Tomsky [57] ABSTRACT A circuit for extending the life of fluorescent tubes 7 Flled' June 1973 driven from a power source subject to interruptions, [21] Appl. No.: 371,414 which includes a uni-directional conducting elements inserted in the line from the power source, a separately powered power source of substantially lower [52] US. Cl 315/86, 315/165, 33ll55//137017, voltage than the main power Source but of Sufficiem voltage to maintain the fluorescent tube in conducg gl i g g tion, a second uni-directional device connected be- 1 0 ears 315/307 tween the secondary power source and the common junction of the first uni-directional device and the load. Further, the circuit may include a voltage sensor [56] References cued to determine whether or not the power is present on UNITED STATES PATENTS the primary power source, a timer to time the length 825,847 7/1906 Lintern 315/86 of time during which power is missing, and means of 3,059,146 /1962 Bond 315/171 disconnecting the secondary power source when such Bogaerts is excessive 3,280,366 10/1966 Ahmed 315/171 3,324,304 6/1967 Duncan 315/86 6 Claims, 4 Drawing Figures T INDEPENDENTLY VOLTAGE T'MER POWERED SENSOR SOURCE Pmmioniw 14 3.858087 SHEET 10F 2 FIG.|

(PRIOR ART) TIMER 0.9Amps l v Voltage W 1 I 44 I [4 I5 I I I I VOL TIMER iiiis I SENSOR SOURCE f 20 I I0 I v I PATENTED EH33 1 I974 SHEET 2 OF 2 42m DEE Q IF CIRCUIT FOR PROLONGING THE LIFE OF FLUORESCENT LAMPS BACKGROUND OF THE INVENTION The invention is directed to means for extending the life of fluorescent tube lamps systems used in railroad and rapid transit applications where the principal power source used comes from a third rail or overhead wire. For example, in the operation of multi-speed traction motors in rapid transit systems, there is available direct current at voltages of 500 to several thousands of volts. Power is appliedto fluorescent lamps through a polarity reverser switch operated by a timer and through conventional starter ballasts and resistors to limit the current drawn through the lamps. The results of prior art systems of the above-described arrangements shown the lamps have significantly or extremely short lamp life from such circuit arrangements of about six months, and if they were used in stationary applications they would have a use life of about three years.

It is found that the resulting short life and the attending difflculty arises from the frequent or repetitive restarting of the lamps, which clearly seems to be due to and caused by gaps in the third rail or overhead lines. The construction of these gaps or breaks in the third rail or overhead lines is essential to and in the application of power in transit applications. Whenever these gaps or breaks are encountered, power is removed from the lines and the electron space between the electrodes of the lamps deionizes. Then when the gaps or breaks are crossed, power is re-applied to the power lines of the lamps and the lamps are re-struck or ignited, during which effect there results invariably a sputtering of the coating of electron-emission material from the electrodes of the lamps. The sputtering then results in darkening of the ends of the lamp tubes and, more importantly, it concludes in the loss of electronemission material from useful location in the lamps and loss of its restarting ability.

After extensive and sufficient loss of material, the lamp becomes incapable of restarting under normally applied voltages, becoming essentially pre-aged, worthless and in need of replacement.

SUMMARY OF THE INVENTION The invention relates to means of extending the life of fluorescent tube lamps when used on railroad and rapid transit applications in which the principal power source used comes from a third rail or overhead wire, or other non-public utility source. More particularly, the invention relates to a device for extending the life of fluorescent tubes driven from an interrupted power source and includes a uni-directional device inserted in the line from the power source, a separately powered power source of substantially lower voltage than the main power source but of sufficient voltage to maintain the fluorescent tube in conduction, a second unidirectional device from the secondary power source connected to the uni-directional device from the first power source at the common junction going to the load, and optionally may include, for example, a voltage sensor or other similar means to determine whether or not the power is present on the primary power source, a timer to time the length of time during which power is missing, and means for disconnecting the secondary power source when such time is excessive.

The invention encompasses a circuit arrangement to avoid battery drain if the main power, for example, the 600V source is lost for a prolonged period of time.

At the time of encountering a gap in the power applied to the lamps, current is immediately replaced at a lower level, but sufficient voltage is always maintained to continue the conduction of the tubes; and when the gap is crossed and power is re-applied, the replacement current supply is removed.

Because there may occur occasions when a gap may persist for a long time, if for example, a train is stopped on a gap and because the independently powered source for cost and compactness reasons should have a limited power capability, it is preferred to use a voltage sensor which will detect the absence of voltage across the lines and start a timer which will time for six or eight seconds. If power is restored to the lines during this time, the timer will reset and not affect the independently powered source. If power is not restored in this period, the timer will cut off the independently powered source and keep it cut off until power is restored to the lines, whereupon the original condition will resume.

BRIEF DESCRIPTION OF THE DRAWING principles of the invention, in which the circuit is interposed at position AA of FIG. 1; and

FIG. 4 is a detailed schematic circuit diagram showing exemplary circuit elements that may be used in the schematic circuit of FIG. 3.

DETAILED DESCRIPTION OF THE INVENTION Referring now to the prior art arrangement shown in FIG. 1, there is shown a direct current line 10 con nected to a suitable source (not shown) for applying direct current operating potential at voltages of 500 volts to several thousand volts to multi-speed traction motors (not shown). The line 10 thus is an input line from which high voltage DC power may be supplied and fed over conductors 12, 14 to lamps 16, 18 through a switch or reverser 20 operated by means of a timer 22 for reversing the high voltage DC power applied to the lamps 16,18. This power brought in through a reverser 20 operated by the timer 22 has the characteristics of causing polarity reversal of the voltage applied to the lamps at periods which may vary from several minutes to several hours. The output on lines 12,14 from the reverser is applied to a plurality of lamps, generally fifteen, or more, but for convenience only two are shown in FIG. 1. The current is normally brought first through a starter ballast 30,32 which forms no part of the invention but is necessary as a means of generating an initial high pulse of the voltage when power is first applied to break doen the lamps in the usual fashion. Current from the ballasts is applied, respectively, through series resistors 34, 36 to limit the current drawn through the lamps and through the fluorescent lamps 16,18 themselves, to the line 14.

It has been shown that extremely short lamp life usually results from this circuit application shown in FIG. 1. Typically, the period is about six months for these lamps that in ordinary stationary applications have a life of about three years or so. The difficulty appears to arise from frequent re-starting of the lamps caused by the gaps in the third rail of overhead lines which, in turn, are essential to provide protection for the transit system. Whenever these gaps are encountered, current is removed from the lines, and the space in the lamps 16, 18 is caused to deionize. When the gap is again crossed, current is re-applied to the lines and the lamp is re-struck. This re-striking invariably sputters some of the electron-emitting material from the tube electrodes resulting over a period of time in darkening the ends of the lamps 16,18 but more importantly, loss of material and loss of re-starting ability. After certain amounts of material is lost from the electrodes, the lamp becomes incapable of starting under the normally applied voltage, becomes worthless, and. needs to be replaced.

In FIG. 2 is shown the volt-ampere characteristics of a fluorescent lamp an with associated series resistance. As can be appreciated from the figure, a fluorescent lamp conducting a direct current behaves effectively as a battery in series with fairly low resistance. Typically, the inherent voltage of a 72 inch, 40 watt fluorescent lamp will be approximately 285 volts. Consequently, it can be maintained in conduction by a voltage of approximately 300 volts or more while drawing much less power than it does from the full 600 volts or more normally applied.

FIGS. 3 and 4 show a schematic and circuit diagram consisting of two isolation diodes or equivalent unidirectional conductors elements 40 and 42 connected in lines 10 as shown and an independently powered DC voltage source 44. Source 44 may be of any suitable type such as a solid state inverter rectifier operating from a storage battery or other source (not shown) which is normally associated with each pair of cars on a railroad or transit system. Alternate sources such as a chemically powered generator or independent highvoltage battery could also be used.

Typically, if the input voltage on lines 10 is 600 volts the independently powered source might be set to 350 volts DC. Under these circumstances during normal contact with the third rail or overhead wire, power will flow from lines 10 through diode 40 to the reversing switch and ballast resistance and lamps exactly as is done in the present system of FIG. 1. Diode 42 is backbiased, and there would be no load on independent source 44. At the time of encountering the gap in the line referred to above, or when current disappears through the diode 40, it is immediately replaced through diode 42 at a lower level, but sufficient voltage is always maintained to continue the conduction of the lamps 16,18. When the gap is crossed and power is reapplied, diode 40 again conducts and diode 42 becomes back-biased unloading the power source 44. There is, however, no restriking of the fluorescent tube, and the life of the tube is thus not impaired. There may occur occasions when such a gap may persist for a long time, for example, if a train is stopped on a gap; and the independently powered source 44 for cost and compactness reasons may often have a limited power capability. In this event, a voltage sensor 14 and timer l5 may also be provided to disconnect source 44 after a preselected brief interval.

FIG. 4 illustrates a preferred embodiment of the invention. One of the third rail terminals 60 is coupled to a transistor coupling network 66 of a voltage sensor network 52 by a timer network 54. The voltage sensor circuit includes signal input conductor 70 connected by the timer 54 to the transistor coupling network 66 for applying the timing signal condition to the base of an NPN transistor 74. When the 600 V condition of the third-rail is lost at terminals, 60,60, after a predetermined time delay the transistor 74 is turned off, turning the transistor 72 to an ON condition, which then turns transistor 76 to an OFF condition. The OFF condition of transistor 76 causes transistor 78 to turn OFF, thus removing power or current from a 20 KHZ oscillator 80 consisting of transistors 82,84. A secondary 86 of the oscillator 80 connected as an output of transistors 82,84 is coupled to a power section 88 of an inverter having a bridge rectifier network associated therewith 92. The bridge network is then connected to the isolation diode 42 described above which terminates in lines 10.

It is thus noted that the voltage sensor 52 responds to the timer 54 in which the charge on capacitor 96 discharges during a period of, for example, several seconds after which the base of NPN transistor 74, is turned OFF. If power or current is restored to lines 10 via terminals 60 during said delay, the timer 54 will reset and not affect the independently powered source 44. If power is not restored within this period, the timer 54 will cutoff the independently powered source 44 and keep it cutoff until power is restored to lines 10 from terminals 60, whereupon the original condition will resume.

In summary, the independently powered source 44 consists of a full wave bridge rectifier 92 driven by a transistor inverter 88 which, in turn, is driven by a transistor oscillator 80. The output of bridge 92 is connected through isolating diode 42, in this case three diodes connected in series with shunts of resistance and capacitance. When 600 volts is present across lines 60 a positive voltage will be present on the base of transistor 74 holding it in a low impedance condition and turning OFF transistor 72. This will result in transistor 76 being turned ON so as to deliver base current to transistor 78 which will also be turned ON and will connect transistors 82 and 84 which comprise the oscillator to the positive battery supply. In this condition the oscillator will operate and the output of the oscillator will be coupled to power amplifier and inverter 88, bridge 92 and through diodes 42 to the junction point. Since 600 Volts is present on the junction from line 60 through diode 40, diode 42 will be back-biased and there will be no loading upon the bridge. Upon loss of power on line 60 capacitor 96 will maintain its charge for a period of time, for example, several seconds. During this time, operation will be as discussed above but since there will no longer by any voltage applied through diode 40, diode 42 will conduct supplying power to maintain the lamps in conduction. When capacitor 96 has discharged sufficiently so that the voltage on the base of transistor 74 is less than the voltage on the base of transistor 72 circuit 66 will flip, transistor 72 will go into its low impedance state turning off transistors 76 and 78 which will turn off the oscillator thereby removing the drive from the power transistors to in effect shut down the auxiliary source. When power is restored the original conditions will resume.

Additional embodiments of the invention in this specification will occur to others and therefore it is intended that the scope of the invention be limited only by the appended claims and not by the embodiment described hereinabove. Accordingly, reference should be made to the following claims in determining the full scope of the invention.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A circuit for prolonging the life of fluorescent lamps operated from a main source of direct current operating potential subject to random, unwanted interruption, comprising input means adapted to be connected at an input terminal with the source; output means adapted to be connected at an output terminal with the lamps; first unidirectional means connected at one end to said input terminal and at the other end to said output terminal for supplying said lamps with operating potential from said main source for normal operation; an auxiliary direct current power source having a voltage less than that of the main source but greater than the extinction voltage of the lamps; and second unidirectional means connected at one end of said auxiliary source and at the other end to said output terminal, said second unidirectional means cooperating with said first unidirectional means for supplying full operating potential to the lamps when the main source is operative and for supplying said lesser operating potential to the lamps from said auxiliary source in response to the occurrence of a random, unwanted interruption of said main source whereby the lamps are precluded from becoming extinguished upon interruption of the main source.

2. The invention according to claim 1 further including voltage sensing means connected between said input means and said auxiliary direct power source and responsive to interruptions in operating potential supplied by the main source to actuate said auxiliary source.

3. The invention according to claim 2 further includ' ing timing means coupled with said voltage sensing means such that said voltage sensing means deactuates said auxiliary source after a predetermined time delay has elapsed following interruption of the main source.

switches coupled in series. 

1. A circuit for prolonging the life of fluorescent lamps operated from a main source of direct current operating potential subject to random, unwanted interruption, comprising input means adapted to be connected at an input terminal with the source; output means adapted to be connected at an output terminal with the lamps; First unidirectional means connected at one end to said input terminal and at the other end to said output terminal for supplying said lamps with operating potential from said main source for normal operation; an auxiliary direct current power source having a voltage less than that of the main source but greater than the extinction voltage of the lamps; and second unidirectional means connected at one end of said auxiliary source and at the other end to said output terminal, said second unidirectional means cooperating with said first unidirectional means for supplying full operating potential to the lamps when the main source is operative and for supplying said lesser operating potential to the lamps from said auxiliary source in response to the occurrence of a random, unwanted interruption of said main source whereby the lamps are precluded from becoming extinguished upon interruption of the main source.
 2. The invention according to claim 1 further including voltage sensing means connected between said input means and said auxiliary direct power source and responsive to interruptions in operating potential supplied by the main source to actuate said auxiliary source.
 3. The invention according to claim 2 further including timing means coupled with said voltage sensing means such that said voltage sensing means deactuates said auxiliary source after a predetermined time delay has elapsed following interruption of the main source.
 4. The invention according to claim 3 wherein said timing means includes a capacitance discharge network.
 5. The invention according to claim 4 wherein said voltage sensing means includes a monostable transistor network responsive to said timing means to control said auxiliary source after said time delay has elapsed.
 6. The invention according to claim 2 wherein said voltage sensing means includes a plurality of transistor switches coupled in series. 